Self-contained paper microfluidic devices can provide inexpensive new tools for rapid diagnostic information in diverse applications such as the healthcare of an individual from a biological fluid or a hazardous chemical in an environment liquid sample. Advantageous elements of paper based microfluidic devices relative to traditional laboratory based diagnostics include the ease of use for individual, rapid diagnostics, lack of sophisticated support equipment, simplified assessment of diagnostic result, low cost, and disposability to prevent contamination.
Since the 1990s, many advances have been made regarding the development of two-dimensional media based microfluidics for the detection of analytes using a variety of fluidic samples. Typically, paper based media, referred to as microfluidic paper analytical devices (MPAD), have been patterned by layering hydrophobic chemistries on hydrophilic media creating physical barriers to contain wicking or capillary fluidic motion. To create microchannel barriers, a variety of technologies and chemistries have been employed.
For example, PCT Patent Application Publication No. WO 2010/022324 discloses methods of patterning hydrophobic materials onto hydrophilic substrates as well as methods of impregnating hydrophilic substrates with a hydrophobic material. U.S. Patent Application Publication No. 2009/0298191 discloses methods of patterning porous media to provide lateral flow and flow-through bioassay devices wherein the devices include a porous, hydrophilic medium and a fluid impervious barrier comprising a polymerizable photoresist, with the barrier substantially permeating the thickness of the porous, hydrophilic medium and defining a boundary of an assay region (containing an assay reagent) within the porous, hydrophilic medium. Other developments have used polystyrene, wax-based and superhydrophobic patterning processes to form physical microchannel barriers defining hydrophilic channels or regions.
U.S. Patent Application Publication No. 2011/0123398 discloses three-dimensional microfluidic devices that include a plurality of patterned porous, hydrophilic layers and a fluid-impermeable layer disposed between adjacent patterned porous, hydrophilic layers. Each patterned porous, hydrophilic layer is disclosed to include a fluid-impermeable barrier that substantially permeates the thickness of the porous, hydrophilic layer and defines boundaries of one or more hydrophilic regions within the patterned porous, hydrophilic layer. The fluid-impermeable layer has openings that are aligned with at least part of the hydrophilic region within at least one adjacent patterned porous, hydrophilic layer.
U.S. Patent Application Publication No. 2008/0025873 discloses microfluidic devices that include a substrate and a non-valve capillary mechanism, as well as a reservoir and one or more channels leading to the reservoir, wherein the non-valve capillary mechanism is within the reservoir, and prevents fluid delivered to the reservoir from wicking from the reservoir into the channels. A delivered fluid is hydrophilically attracted to and retained within the reservoir.
In other devices, processes employed to delay fluidic motion have been based on abruptly changing the physical geometry of the microchannels through enlargement of the microchannel. Assembling two or more multiple delay valves to form a joined region where at least two fluids were required to advance the fluid created a temporary trigger valve having a longer delay time. In still other devices, paraffin wax has been used to restrict wicking through a control point between layers.
Although these devices may prevent undesired mixing of fluids between reservoirs and adjacent channels, the need remains for the ability to control mixing of fluids with a microfluidic valve that does not employ mechanical or electrical mechanisms to control the valve thereby restricting the utility of the device and its stand alone use.